Why can't my textures fit on a single atlas in Sprite Packer?

I’ve created a new project for iOS with three textures (all 720x1024). I would expect that they can fit on a single 2048x2048 atlas when packed using Sprite Packer but it consistently produces two textures - a 2048x2048 for two of the textures and a third 1024x1024 for the last texture. I’ve tried both the Default and Tight packer policy without luck.

My Texture Import Settings are set to Advanced…
Generate Mip Maps: No
Mesh Type: Full Rect (I don’t think this matters for Image?)
Extrude Edges: 0
Override for iPhone:
Max Size: 2048
Format: RGB Compressed PVRTC 4 bits

Am I doing something wrong or is this a bug? I am currently on Unity 5.1.1f1.

2279127–152994–Atlas Test.zip (40.6 KB)

Update - I downloaded Unity 5.1.3.f1 and the problem remains.

Update - I went ahead and filed a bug: Case 724839
https://fogbugz.unity3d.com/default.asp?724839_7rllapbft3tu137d